Hydrotreating of heavy crude oils and residues is difficult due to the presence of refractory compounds of high molecular weight. Hydrotreating of heavy crude oils and residues depends on factors such as the catalyst used, the type of feed to be treated and the design of the reactors. In the hydrotreating process, the catalysts are designed to remove heteroatoms such as sulfur, nitrogen, and metals. The removed sulfur and nitrogen leave the system as gaseous products while metals are deposited irreversibly on the catalyst causing its permanent deactivation.
The design of catalysts for all reactions involved in heavy crude oil hydrotreating is a challenge because the large and complex molecules that contain the heteroatoms present diffusion problems in the pores of the catalyst and inhibit the adsorption of other reagents in its active sites. The task becomes even more problematic due to the presence of asphaltenes that cause the formation of coke deposits and deactivate the catalyst faster.
In general, the literature suggests the use of CoMo and NiMo catalysts supported on alumina.
The properties of the catalysts used depend on the type of feed to be processed. Operating conditions for heavy crudes are more severe than in the case of middle distillates where operating conditions are from moderate to low. Therefore, the catalysts chemical and physical properties, such as pore diameter, surface area, pore volume distribution, and surface acidity among others, must be different.
Currently, some hydrotreating processes in fixed bed reactors are using combinations of different catalysts and metal guard materials. These processes can contain several reactors including a guard bed reactor. Each reactor contains catalysts for different purposes. For example, in the literature it is claimed the use of a combination of more than ten catalysts. Some porous solids such as activated bauxite and alumina have been used as metal guards. Metals and clays present in the feed, cause a higher pressure drop during operation. This problem can be overcome by using a guard bed reactor.
There are patent documents which claim the use of Mo with Ni and/or Co. While others include the use of compounds of groups IA, IIA, VA, VIIA, IIB, IVB, VB, and VIIB using different types of oxides such as alumina, zeolites, silica, silica-alumina, titania, and/or combinations of them. Some of these patent documents are described below.
U.S. Pat. No. 6,399,530 discloses an amorphous silica/alumina with large surface area, and pore volume, and adequate silica content, to ensure the desired acidic function for chemical reactions. Silica/alumina is used as support in the preparation of the hydrocracking catalysts having high activity and selectivity towards middle distillates. The catalyst also contains metallic components and a modified ultrastable Y zeolite.
Likewise, U.S. Pat. No. 5,620,590 discloses a catalyst consisting of a combination of hydrogenating metals (Co—Mo, Ni—Mo, Ni—W, and Ni—W—Co), and alpha alumina with ultrastable Y zeolite with crystal size between of 0.1-0.5 micron, cell unit of 24.2-24.4 angstroms. The feeds used in the cracking process having an API gravity in the range of 22 to 31.9°.
U.S. Pat. No. 4,988,659 discloses the preparation of a catalyst composed of co-gels of silica/alumina with high surface area, which contributes to increase both, the activity and the octane number in gasoline. It also increases the production of light cycle oil, decreases the production of heavy cycle oil, and increases the quality of both. The co-gels can be combined with other components such as zeolites, sieves such as beta, SAPO's, ALPO's, etc. clays, modified clays, inorganic oxides, metals, coal, and organic substances, etc.
U.S. Pat. No. 4,894,142 discloses a catalyst which consists of a mixture of i) a hydrogenation metal of groups VI and VIII of the periodic table (Mo, W, Ni, Co), ii) a matrix of a refractory inorganic oxide composite silica-alumina (45-90%) and alumina (5-45%), iii) crystalline silicoaluminate (zeolite HY, 2-20%) with unit cell in the range 24.2 to 24.4 angstrom. The catalyst is highly selective to the conversion of heavy hydrocarbons to middle distillates in a temperature range of 149-371° C. The feeds used can be diesel, vacuum gas oils, demetallizated products, atmospheric residue, de-asphalted vacuum residue, and bituminous oils. Preferably gas oil mixtures containing 50% volume of their components with boiling point above 371° C. These feeds contain nitrogen compounds usually present as organonitrogen compounds in amounts of 1 wppm to 1.0 wt %. They, also contain enough sulfur compounds to present sulfur contents greater than 0.15 wt %. The catalysts of this invention are characterized by having low acidity, measured by temperature programmed desorption of ammonia (NH3-TPD), which in this case was 1.50.
On the other hand, U.S. Pat. No. 4,818,739 discloses the use of hydrocracking catalysts for feeds with a boiling point between 198.7 to 347.7° C. The catalysts are comprised of at least one non-zeolitic molecular sieve (NZ-MS) for the hydrocracking process based on silicoaluminophosphates like SAPO, ELAPSO, MeAPO, FeAPO, TiAPO, FCAPO, and ELAPO. At least one zeolitic aluminosilicate, which may consist of a Y zeolite, ultrastable Y zeolite, X zeolite, beta zeolite, KZ-20 zeolite, faujasite, LZ-210, LZ-10, ZSM, and a mixture of them containing (0.1 to 20 wt %) rare earths of the groups IIA, IIIA, IIIB, and VIIB or mixtures of them. Besides, at least a matrix of a refractory inorganic oxide, which may be clays, silicas, aluminas, silica-alumina, silica-zirconia, silica-magnesia, alumina-boria, alumina-titania, and a mixture of them. Also, a hydrogenating component added by impregnation, which can be cobalt, nickel, and/or molybdenum. The products of this process are characterized for having a high ratio of iso-paraffins/n-paraffins
U.S. Pat. No. 4,689,137 discloses a catalyst composed of a crystalline aluminosilicate (Y zeolite), with silica/alumina ratio above 6.2, in combination with a refractory porous inorganic oxide. The Y Zeolite contains rare earths and noble metals (Group VIII), which are incorporated using the ion exchange method. The combination of zeolite and refractory oxide contains from 4.5 to 6.9 wt % of water, which is necessary thus the catalyst exhibits a high activity in the hydrocracking reactions. The Y zeolite used as part of the catalyst was prepared by ammonium exchange with a solution of ammonium fluorosilicate.
U.S. Pat. No. 4,604,187 discloses a catalyst containing a Y zeolite. The Y zeolite was prepared by exchanging a sodium zeolite with cations of one or more rare earth elements, followed by calcination, ammonia exchange and ion exchange of cations of noble metals of Group VIII. The resulting zeolite is not only highly active to promote catalytic hydrocracking reactions but also after the reaction it can be regenerated by coke combustion.
U.S. Pat. No. 4,422,959 relates to the preparation of a catalytic composite comprising a silica-alumina support with silica content of 20 to 80 wt %. In combination with nickel and vanadium compounds of a concentration in the range of 0.1-10 wt %. The feed used are hydrocarbons or mixtures of hydrocarbons that are in a range of boiling temperatures of 200-650° C. It can also be used hydrocarbons from tar sands.
U.S. Pat. No. 4,419,271 relates to a hydrocracking process with a catalyst. The hydrocracking catalyst improves the activity, selectivity and stability producing middle distillates from heavy gas oils. The catalyst comprises hydrogenation compounds such as metals of groups VIII mainly cobalt or nickel in combination with Group VI metals such as molybdenum or tungsten sulfides on a refractory oxide support such as alumina, magnesia, silica-alumina, and zeolite-type crystalline aluminosilicate with high cracking activity such as Y zeolite or rare earths-exchanged Y zeolite. They also have excellent activity for hydrodenitrogenation and hydrodesulfurization.
U.S. Pat. No. 4,111,846 discloses the preparation of inorganic hydrosols, particularly titania-alumina-silica hydrosols that serve as binders for catalytic compositions. The composition of the catalysts for the conversion of hydrocarbons finally comprises inorganic materials such as clays, and crystalline aluminosilicates known as zeolites, aggregates of discrete particles in the range from 20 microns to 6 mm in size. These catalysts may have a porous structure that allows the reactant molecules to enter into the catalyst particles. At the same time the catalyst particles have the physical strength and density characteristics that allow its use in commercial processes.
U.S. Pat. No. 3,304,254 discloses the improvement of a hydrotreating catalyst, characterized by a physical mixture of (1) a crystalline aluminosilicate with low sodium content (<4%), and (2) a hydrogenation component which comprises, in greater proportion, a porous support (crystalline aluminosilicate), and in lower proportion a component exhibiting hydrogenation activity such as elements of groups VI and VIII of the periodic table, especially Co (1-8 wt %) and MoO3 (3-20 wt %). The high molecular weight hydrocarbons or a hydrocarbon mixture, for example, a petroleum fraction is subjected to cracking in the presence of hydrogen and catalyst. This process is carried out at temperatures in the range 427-593° C. This process has the disadvantage of producing large amounts of dry gas and an excess of butane.
U.S. Pat. No. 3,459,680 relates to a process to convert organic compounds in the presence of acidic catalytic sites. Such conversion processes include hydrocracking, alkylation, isomerization, polymerization, etc. This process relates to an improved composite, which comprises a crystalline aluminosilicate with an ordered structure with three-dimensional network characterized because the pores have a uniform diameter in the range of 4 to 15 angstroms. The remaining composite is comprised of a crystalline aluminosilicate, but it may be non-porous or catalytically inert. The rest of the remaining composite also contains a porous material. The composite is prepared by mechanical mixing. These catalysts have attrition resistance, activity, selectivity, and stability for steam deactivation.
U.S. Pat. No. 3,969,222 relates to a hydrotreating process (hydroprocessing) of hydrocarbons or mixtures of them, using a catalytic composite of a porous material, a component of palladium or platinum, a component of iridium and a component of germanium. The composite comprises a crystalline aluminosilicate. This process also is directed to the hydrogenation of aromatic rings, ring opening of cyclic hydrocarbons, desulfurization, denitrogenation, hydrogenation, etc. This process consists of two stages; the catalyst is for the second stage where the feed used already passed through the first stage.